This invention relates to a spray head for an aerosol container, comprising a connecting bore for sealingly receiving a delivery tube stub of an aerosol valve; a spray orifice; a main chamber connecting said connecting bore and said spray orifice; a piston member disposed in said main chamber and presenting a needle member cooperating with said spray orifice; and spring means urging said piston member to said spray orifice, said spray orifice being sealed by the end of said needle member in an inoperative position, and the piston member being arranged to move against the force exerted by said spring means under the influence of an elevated pressure prevailing in said main chamber, whereby the spray orifice is cleared by said needle member.
A spray head of this kind is disclosed in U.S. Pat. No. 4,182,496. Under the influence of the force exerted by the spring means on the piston member, the needle member cooperating with the spray orifice seals the spray orifice so long as the spray head is not operated. As soon as the spray head is operated with the finger, in the usual way, an open connection is formed, also in the usual way, between the interior of the container on which the spray head is mounted and the connecting duct and the chamber of the spray head. As a result, the pressure in the chamber rises and the piston member is moved away from the spray orifice against the force exerted by the spring means. The spray orifice is thus cleared by the needle member, and the product can exit from the container.
After termination of a spray operation, product residues remaining behind in the connecting duct and the chamber are effectively sealed from the outside air by the needle member cooperating with the spray orifice, and consequently cannot dry up and render the spray canister unsuitable for use. It is only between the needle member and the walls of the spray orifice that a minor quantity of product could be deposited, as a result of which the needle member could become stuck. The small contact area between the needle member and the spray orifice, however, ensures that the force exerted on the piston member when the spray head is operated is sufficiently large enough for the needle member to be pulled out of the spray orifice even then.
A spray head of this kind is particularly suitable for use in environmentally friendly low-propellant fluid dispensers such as aerosol containers. Unlike conventional aerosol containers, in low-propellant spray canisters the propellant is not permitted to leave the container. Consequently, the spray head of the dispenser must not be flushed with propellant in the usual way by holding the container upside down and operating the spray head with the finger. Indeed, in many low-propellant spray canisters, as described, for example, in U.S. Pat. No. 5,005,738, this is impossible, because means are provided to ensure that the propellant cannot exit from the container in any position the container occupies.
A problem which does occur in low-propellant spray canisters is that the spray dispensed is rather wet, which means that there is insufficient atomization. This problem can be solved to a certain extent by using a swirl chamber which is passed by the product being sprayed just before it reaches the spray orifice. Such a swirl chamber is shown in U.S. Pat. No. 4,182,496, but practice has shown that, even when a swirl chamber is used, in which the product is, so to say, mixed with gas, the resulting spray is still too wet with many products, such as paint.